Field of the Invention
The invention relates to a method of aligning stacked or piled sheets in a feeder of a sheet-processing machine, wherein a sheet to be separated is pivotable about a vertical axis extending orthogonally to a transport direction of the sheet, as viewed in the transport direction thereof, in order to correct a skewed position of a leading edge thereof, relative to at least one front lay. The invention also relates to a device for performing the method, including a sheet lifting device for lifting a sheet resting on the top of the stack or pile and for pivoting the sheet about a vertical axis extending to the transport direction of the separated sheet.
Aligning devices and methods implementable therewith, which are of the aforementioned type, have become known heretofore from the published German Patent Document DE 44 10 529 C2. The aligning device is employed in the feeder of a sheet-fed printing machine and is used for precise alignment of a sheet lifted off a sheet pile on a transport path of the sheet from the sheet pile to front lays engaged thereby, the front lays serving to ensure a perpendicular alignment of the sheet leading edge to the transport direction of the sheet, and side lays for exactly positioning the sheet in the printing unit. The aligning device has a sheet lifting device by which the uppermost sheet, respectively, on the sheet pile, is lifted at the trailing region thereof and is pivotable about a vertical axis extending perpendicularly to the transport direction of the sheet, in order to compensate for a skewed position of the sheet. After the sheet has been moved into engagement with the front lays, it is shifted transversely with respect to the transport direction until it comes into contact with the side lays. The lateral displacement path of the sheet depends upon their skewed position on the sheet pile, which means that the greater the skewed position of the sheet resting on the sheet pile, which is to be compensated for by pivoting the sheet about the vertical axis thereof as the sheet is lifted from the sheet pile, the greater is the lateral displacement path towards the side lays. Depending upon the direction of the skewed position, the displacement path can be longer or shorter. However, because the time window for the alignment of each sheet on the front and side lays is of equal length for each sheet, the displacement path should be kept approximately constant, because otherwise, depending upon the direction, the time window for lateral alignment may no longer be sufficient, or the sheet can remain caught on the side lay.
It is therefore an object of the invention to provide a method and a device for aligning stacked or piled sheets in a feeder of a sheet-processing machine, of the type mentioned in the introduction hereto, wherein it is possible to ensure that the sheets lifted off the sheet pile, after the alignment of the leading edge thereof, are aligned perpendicularly to the transport direction, and that the lateral displacement path of the sheets towards the side lay is at least approximately equal in length for all of the sheets, regardless of the magnitude of the skewed position thereof before the alignment.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of aligning stacked or piled sheets in a feeder of a sheet-processing machine, wherein a sheet to be separated is pivotable about a vertical axis extending orthogonally to a transport direction of the sheet, as viewed in the transport direction, in order to correct a skewed position of a leading edge thereof relative to at least one front lay. The method comprises determining, relative to the front lay, a skewed position of sheets present at the front lay or on the top of the sheet pile, and displacing, transversely to the transport direction, with the sheet pile, before the sheet is lifted therefrom, or the sheet lifted off the sheet pile, depending upon the determined skewed position, over a displacement distance that is of such length that, after the skewed-position correction, there is a defined spaced distance between a side edge of the sheet and at least one side lay.
In accordance with another mode of the method invention, the defined spaced distance, after the skewed-position correction, is of equal length for all of the separated sheets, respectively.
In accordance with a further mode, the method of the invention includes determining the skewed position of the sheet visually by an operator.
In accordance with an added mode, the method of the invention includes defining by the operator an adjustment angle by which the sheet to be aligned is pivoted about the vertical axis for the purpose of correcting the skewed position.
In accordance with an additional mode, the method of the invention includes determining the displacement distance in accordance with an adjustment angle.
In accordance with yet another mode, the method of the invention includes calculating the displacement distance in accordance with an adjustment angle.
In accordance with yet a further mode, the method of the invention includes automatically registering the skewed position of the sheet with the aid of at least one sensor.
In accordance with yet an added mode, the method of the invention includes calculating by a control and/or regulating device the necessary correction of the skewed position of the sheet in accordance with the determined skewed sheet position.
In accordance with yet an additional mode, the method of the invention includes calculating the displacement distance in accordance with the value of the skewed-position correction.
In accordance with still another mode, the method of the invention includes activating by the control and/or regulating device actuators associated with the sheet pile and the sheet lifted off the sheet pile in accordance with the calculated skewed-position correction value and the displacement distance.
In accordance with another aspect of the invention, there is provided a device for aligning stacked sheets in a feeder of a sheet-processing machine, including a sheet lifting device for lifting a sheet resting on the top of a sheet stack or pile and for pivoting the sheet about a vertical axis extending at least approximately orthogonal to the transport direction of the separated sheet, comprising at least one of a pile displacement device for displacing the sheet pile at least approximately transversely to the transport direction of the separated sheets and of at least one lifting element that is displaceable at least transversely to the transport direction of the separated sheets.
In accordance with a concomitant feature of the invention, the aligning device includes a control and/or regulating device for respectively controlling/regulating the pivoting of the sheet, and the displacement of the sheet pile transversely to the transport direction of the separated sheets.
In order to achieve the object of the invention, a method is thus proposed, which is distinguished by the fact that the skewed position of the sheets arriving at or present at the front lay or of the sheet resting or present at the top of the pile is determined relative to the front lay, and that the pile, before the sheet is lifted therefrom, and/or the sheet lifted off the pile is displaced transversely or virtually transversely to the transport direction, depending upon the determined skewed position, over a displacement distance, that is of such length that, following the skewed-position correction, there is a defined distance between a side edge of the sheet and at least one side lay.
According to a first alternative, therefore, provision is made for the entire sheet pile to be moved transversely to the transport direction of the sheets a displaced distance which depends upon the skewed position of the sheets arriving at the front lay or of the sheet resting at the top of the sheet pile, so that after the sheet has been lifted off the sheet pile and after the skewed-position correction thereof, which is implemented by appropriate pivoting of the sheet about a vertical axis so that the leading edge of the sheet extends perpendicularly to the transport direction of the sheets, there is approximately a preselectable or predefined distance between the side edge of the sheet and the side lay.
In another alternative, only the lifted top sheet is shifted a given amount corresponding to the displacement distance transversely to the transport direction, it being possible for this to be done before, during or after the skewed-position correction.
According to a third alternative, provision is made for both the sheet pile, while the top sheet is still resting on the latter, and the sheet itself, after the latter has already been lifted off the sheet pile, respectively, to be shifted over respective given partial distances which, when added vectorially, result precisely in the displacement distance, so that after the skewed-position correction, the sheet side edge is at a desired spaced distance from the side lay.
The common feature in all of the alternatives is that the spaced distance of the sheet from the side lay can be varied or preselected or defined. Particular preference is given to the procedure wherein the skewed position is determined when a sheet arrives at the front lay and is used to determine a trend in the skewed position. This trend is the starting information for the lateral shift over the displaced distance.
In a particularly preferred alternative, provision is made for the spaced distance, with regard to all of the separated sheets, to be equal in length, after the skewed-position correction. Therefore, the time wherein the aligned sheet is shifted or pulled laterally in the direction of the side lay is preferably of equal length for all of the sheets, regardless of the respective skewed position thereof on the sheet pile.
In order to achieve the object of the invention, a device for aligning stacked sheets in a feeder of a sheet-processing machine is also proposed. This device according to the invention includes a pile or stack displacement device for displacing the sheet pile or stack transversely or approximately transversely with respect to the transport direction of the separated sheets. Alternatively or additionally, the sheet lifting device has at least one lifting element which is displaceable transversely or approximately transversely with respect to the transport direction of the separated sheets and which, for example, can be constructed as a sucker. With the aid of the stack or pile displacement device and the sheet lifting device with the displaceable lifting element thereof, an alignment of the respective top sheet of the sheet pile or stack transversely with respect to the transport direction is possible in a desired manner, so that following a skewed-position correction of the lifted sheet, in the case of all sheets it is possible to implement an equally large distance between the sheet side edge and a side lay, regardless of the magnitude of the respective skewed position of the sheets before the skewed-position correction thereof.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for aligning stacked sheets in the feeder of a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: